This invention relates to an electrosurgical instrument for the treatment of tissue in the presence of an electrically conductive fluid medium, to electrosurgical apparatus including such an instrument, and to an electrode unit for use in such an instrument. Endoscopic electrosurgery is useful for treating tissue in cavities of the body, and is normally performed in the presence of a distension medium. When the distension medium is a liquid, this is commonly referred to as underwater electrosurgery, this term denoting electrosurgery in which living tissue is treated using an electrosurgical instrument with a treatment electrode or electrodes immersed in liquid at the operation site. A gaseous medium is commonly employed when endoscopic surgery is performed in a distensible body cavity of larger potential volume in which a liquid medium would be unsuitable, as is often the case in laparoscopic or gastroenterological surgery.
Underwater surgery is commonly performed using endoscopic techniques, in which the endoscope itself may provide a conduit (commonly referred to as a working channel) for the passage of an electrode. Alternatively, the endoscope may be specifically adapted (as in a resectoscope) to include means for mounting an electrode, or the electrode may be introduced into a body cavity via a separate access means at an angle with respect to the endoscopexe2x80x94a technique commonly referred to as triangulation. These variations in technique can be subdivided by surgical speciality, where one or other of the techniques has particular advantages given the access route to the specific body cavity. Endoscopes with integral working channels, or those characterised as resectoscopes, are generally employed when the body cavity may be accessed through a natural openingxe2x80x94such as the cervical canal to access the endometrial cavity of the uterus, or the urethra to access the prostate gland and the bladder. Endoscopes specifically designed for use in the endometrial cavity are referred to as hysteroscopes, and those designed for use in the urinary tract include cystoscopes, urethroscopes and resectoscopes. The procedures of transurethal resection or vaporisation of the prostate gland are known as TURP and EVAP respectively. When there is no natural body opening through which an endoscope may be passed, the technique of triangulation is commonly employed. Triangulation is commonly used during underwater endoscopic surgery on joint cavities such as the knee and the shoulder. The endoscope used in these procedures is commonly referred to as an arthroscope.
Electrosurgery is usually carried out using either a monopolar instrument or a bipolar instrument. With monopolar electrosurgery, an active electrode is used in the operating region, and a conductive return plate is secured to the patient""s skin. With this arrangement, current passes from the active electrode through the patient""s tissues to the external return plate. Since the patient represents a significant portion of the circuit, input power levels have to be high (typically 150 to 250 watts), to compensate for the resistive current limiting of the patient""s tissues and, in the case of underwater electrosurgery, power losses due to the fluid medium which is rendered partially conductive by the presence of blood or other body fluids. Using high power with a monopolar arrangement is also hazardous, due to the tissue heating that occurs at the return plate, which can cause severe skin burns. There is also the risk of capacitive coupling between the instrument and patient tissues at the entry point into the body cavity.
When performing surgery in body cavities, vital structures often lie in close proximity to the site of application, and these structures may be damaged by the collateral spread of the electrosurgical effect. Also of concern when using monopolar electrosurgery is that the operating voltage is elevated to overcome the resistive current limiting of the patient""s tissues or to overcome carbonisation of the application electrode. Arcing by direct coupling to adjacent structures, or through breaches in insulation, may produce accidental tissue damage outside the narrow field of view of the endoscope. There is also the risk of capacitive coupling between the instrument and the patient""s tissues at the entry point into the body cavity such that an electrosurgical energy may be coupled to tissue at the entry point. This coupled energy can sometimes be sufficient to cause burning. These risks of using monopolar electrosurgery during endoscopic procedures are now well recognised, and have driven a move towards adoption of bipolar surgery.
With bipolar electrosurgery, a pair of electrodes (an active electrode and a return electrode) are used together at the tissue application site. This arrangement has advantages from the safety standpoint, due to the relative proximity of the two electrodes so that radio frequency currents are limited to the region between the electrodes. However, the depth of effect is directly related to the distance between the two electrodes; and, in applications requiring very small electrodes, the inter-electrode spacing becomes very small, thereby limiting tissue effect and output power. Spacing the electrodes further apart would often obscure vision of the application site, and would require a modification in surgical technique to ensure correct contact of both electrodes with tissue.
There are a number of variations to the basic design of the bipolar probe. For example, U.S. Pat. No. 4,706,667 describes one of the fundamentals of the design, namely that the ratio of the contact areas of the return electrode and of the active electrode is greater than 7:1 and smaller than 20:1 for cutting purposes. This range relates only to cutting electrode configurations. When a bipolar instrument is used for desiccation or coagulation, the ratio of the contact areas of the two electrodes may be reduced to approximately 1:1 to avoid differential electrical stresses occurring at the contact between the tissue and the electrodes.
The electrical junction between the return electrode and the tissue can be supported by wetting of the tissue by a conductive solution such as normal saline. Both monopolar and bipolar probe arrangements often provide a means of suction and irrigation, primarily intended to wash the operative site. In such a case, the active electrode is retracted within the irrigation sheath to enable direct contact of the sheath with the tissue without the risk of mechanical damage to the tissue by the exposed electrode. No surgical effect can be produced with the electrode retracted, or during the passage of saline. As a secondary benefit, this arrangement allows the wetting of tissue to reduce contact impedance.
In bipolar needle arrangements, one of the obvious limitations is that the active electrode must be completely buried in the tissue to enable the return electrode to complete the circuit. Another problem is one of orientation: even a relatively small change in application angle from the ideal perpendicular contact with respect to the tissue surface, will change the electrode contact area ratio, so that a surgical effect can occur in the tissue contacting the return electrode.
Cavity distension provides space for gaining access to the operation site, to improve visualisation, and to allow for manipulation of instruments. In low volume body cavities, particularly where it is desirable to distend the cavity under higher pressure, liquid rather than gas is more commonly used due to better optical characteristics, and because it washes blood away from the operative site.
Conventional underwater electrosurgery has been performed using a non-conductive liquid (such as 1.5% glycine) as an irrigant, or as a distension medium to eliminate electrical conduction losses. Glycine is used in isotonic concentrations to prevent osmotic changes in the blood when intra-vascular absorption occurs. In the course of an operation, veins may be severed, with resultant infusion of the liquid into the circulation, which could cause, among other things, a dilution of serum sodium which can lead to a condition known as water intoxication.
The applicants have found that it is possible to use a conductive liquid medium, such as normal saline, in underwater endoscopic electrosurgery in place of non-conductive, electrolyte-free solutions. Normal saline is the preferred distension medium in underwater endoscopic surgery when electrosurgery is not contemplated, or a non-electrical tissue effect such as laser treatment is being used. Although normal saline (0.9% w/v; 150 mmol/l) has an electrical conductivity somewhat greater than that of most body tissue, it has the advantage that displacement by absorption or extravasation from the operative site produces little physiological effect, and the so-called water intoxication effects of non-conductive, electrolyte-free solutions are avoided.
Carbon dioxide is the preferred gaseous distension medium, primarily because of its non-toxic nature and high water solubility.
In endoscopic procedures in which the distension medium is a gas, the applicants have found that it is possible to use an electrically-conductive gas (such as argon) in place of carbon dioxide. Argon is conductive when excited into a discharge state, and has been employed in both endoscopic and conventional monopolar electrosurgery as a method of increasing the distance between the tissue and the instrument, by providing a conductive path between the two when high voltage electrosurgical ouputs such as spray or fulgurate are being used. The high voltages used in this application result in a very low penetration of the electrosurgical effect into the tissue, making the technique only suitable to control bleeding from multiple small blood vessels. This allows the surgeon to stanch bleeding from multiple sites in a surgical wound using a rapid xe2x80x9cpaintingxe2x80x9d technique, rather than applying electrosurgery to each individual bleeding site. The argon gas is delivered through a hollow surgical instrument, and passes over the monopolar electrode exposed at the tip of the instrument as a stream. This produces a region at the operative site which is rich in argon, and which contributes to the distension of the body cavity. High voltage monopolar electrosurgical outputs are undesirable in endoscopic surgery, because of the risks of damaging structures outside the field of vision, by either capacitive or direct coupling to a portion of the instrument remote from the operative site often outside the field of vision of the operator.
The applicants have developed a bipolar instrument suitable for underwater electrosurgery using a conductive liquid or gaseous medium. This electrosurgical instrument for the treatment of tissue in the presence of a fluid medium, comprises an instrument body having a handpiece and an instrument shaft and an electrode assembly, at one end of the shaft. The electrode assembly comprises a tissue treatment electrode which is exposed at the extreme distal end of the instrument, and a return electrode which is electrically insulated from the tissue treatment electrode and has a fluid contact surface spaced proximally from the exposed part of the tissue treatment electrode. In use of the instrument, the tissue treatment electrode is applied to the tissue to be treated whilst the, return electrode, being spaced proximally from the exposed part of the tissue treatment electrode, is normally spaced from the tissue and serves to complete an electrosurgical current loop from the tissue treatment electrode through the tissue and the fluid medium. This electrosurgical instrument is described in the specification of the applicants co-pending British Patent Application No. 9512889.8.
The electrode structure of this instrument, in combination with an electrically conductive fluid medium largely avoids the problems experienced with monopolar or bipolar electrosurgery. In particular, input power levels are much lower than those generally necessary with a monopolar arrangement (typically 100 watts). Moreover, because of the relatively large spacing between its electrodes, an improved depth of effect is obtained compared with conventional bipolar arrangement.
The aim of a first aspect of the invention is to provide an improved electrosurgical instrument of this type.
The present invention provides an electrosurgical instrument for the treatment of tissue in the presence of an electrically-conductive fluid medium, the instrument comprising an instrument shaft, and an electrode assembly at one end of the shaft, the electrode assembly comprising a tissue treatment electrode and a return electrode which is electrically insulated from the tissue treatment electrode by means of an insulation member, the tissue treatment electrode being exposed at the distal end portion of the instrument, and the return electrode having a fluid contact surface spaced proximally from the exposed end of the tissue treatment electrode by the insulation member, wherein the exposed end of the tissue treatment electrode is constituted by a plurality of tissue treatment filamentary members made of an electrically-conductive material, the filamentary members being electrically connected to a common electrical supply conductor.
The return electrode is spaced from the tissue treatment electrode so that, in use, it does not contact the tissue to be treated, and so that the electrical circuit is always completed by the conductive fluid, and not simply by arcing between the electrodes. Indeed, the arrangement is such that arcing between the adjacent parts of the electrode assembly is avoided, thereby ensuring that the tissue treatment electrode can become enveloped in a vapour pocket so that tissue entering the vapour pocket becomes the preferred path for current to flow back to the return electrode via the conductive fluid,
In a preferred embodiment, a plurality of separate, individual filaments constitute the filamentary members. Advantageously, the filaments each have a length lying within the range of from 0.5 mm to 5 mm, in which case the instrument is used for tissue removal by vaporisation. Preferably, the filaments each have a diameter lying within the range of from 0.05 mm to 0.3 mm.
Alternatively, a single coiled filament constitutes the filamentary members, the coils of the filament constituting the filamentary members.
Preferably, the filamentary members extend longitudinally from the extreme distal end of the instrument. Alternatively, the filamentary members extend laterally through a cut-out formed in a side surface of the insulation member adjacent to the distal end thereof. Conveniently, the return electrode is formed with a hood-like extension which extends over the surface of the insulation member which is opposite the cut-out.
In another preferred embodiment, the filamentary members are mounted within the insulation member in such a manner that they are axially movable relative to the insulation member between a first operating position, in which they extend partially from the insulation member, and a second operating position, in which they extend fully from the insulation member. In this case, the instrument can be used for tissue removal by vaporisation when the filaments are in the first operating position, and for desiccation when the filaments are in the second operating position.
Advantageously, the common electrical supply conductor is a central conductor, the insulation member surrounding the central conductor.
The filamentary members may be made from a precious metal such as platinum or from a platinum alloy such as platinum/iridium, platinum/tungsten or platinum/cobalt. The filamentary members could also be made of tungsten. The insulation member may be made of a ceramic material, silicone rubber or glass.
Where the filamentary members are separate individual filaments, they may each have a length lying within the range of from 5 mm to 10 mm. In this case, they may be made of stainless steel.
In yet another preferred embodiment, the insulation member is formed with at least one wing, the or each wing extending distally from the insulation member to project beyond the tissue treatment electrode. Preferably, the insulation member is formed with a pair of diametrically-opposed wings.
The invention also provides an electrode unit for an electrosurgical instrument for the treatment of tissue in the presence of an electrically-conductive fluid medium, the electrode unit comprising a shaft having at one end means for connection to an instrument handpiece, and, mounted on the other end of the shaft, an electrode assembly comprising a tissue treatment electrode and a return electrode which is electrically insulated from the tissue treatment electrode by means of an insulation member, the tissue treatment electrode being exposed at the distal end portion of the instrument, and the return electrode having a fluid contact surface spaced proximally from the exposed end of the tissue treatment electrode by the insulation member, wherein the exposed end of the tissue treatment electrode is constituted by a plurality of tissue treatment filamentary members made of an electrically-conductive material, the filamentary members being electrically connected to a common electrical supply conductor.
The invention further provides electrosurgical apparatus comprising a radio frequency generator and an electrosurgical instrument for the treatment of tissue in the presence of an electrically-conductive fluid medium, the instrument comprising an instrument shaft, and an electrode assembly at one end of the shaft, the electrode assembly comprising a tissue treatment electrode and a return electrode which is electrically insulated from the tissue treatment electrode by means of an insulation member, the tissue treatment electrode being exposed at the distal end portion of the instrument, the return electrode having a fluid contact surface spaced proximally from the exposed end of the tissue treatment electrode by the insulation member, and the radio frequency generator having a bipolar output connected to the electrodes, wherein the exposed end of the tissue treatment electrode is constituted by a plurality of tissue treatment filamentary members made of an electrically-conductive material, the filamentary members being electrically connected to the radio frequency generator by a common electric supply conductor.
Electrosurgical instruments of the invention are useful for dissection, resection, vaporisation, desiccation and coagulation of tissue and combinations of these functions with particular application in hysteroscopic surgical procedures. Hysteroscopic operative procedures may include: removal of submucosal fibroids, polyps and malignant neoplasms; resection of congenital uterine anomalys such as septum or subseptum; division of synechiae (adhesiolysis); ablation of diseased or hypertrophic endometrial tissue; and haemostasis.
The instruments of the invention are also useful for dissection, resection, vaporisation, desiccation and coagulation of tissue and combinations of these functions with particular application in arthroscopic surgery as it pertains to endoscopic and percutaneous procedures performed on joints of the body including, but not limited to, such techniques as they apply to the spine and other non-synovial joints. Arthroscopic operative procedures may include: partial or complete meniscectomy of the knee joint including meniscal cystectomy; lateral retinacular release of the knee joint; removal of anterior and posterior cruciate ligaments or remnants thereof; labral tear resection, acromioplasty, bursectomy and subacromial decompression of the shoulder joint; anterior release of the temperomandibular joint; synovectomy, cartilage debridement, chondroplasty, division of intra-articular adhesions, fracture and tendon debridement as applied to any of the synovial joints of the body; inducing thermal shrinkage of joint capsule as a treatment for recurrent dislocation, subluxation or repetitive stress injury to any articulated joint of the body; disectomy either in the treatment of disc prolpase or as part of a spinal fusion via a posterior or anterior approach to the cervical, thoracic and lumbar spine or any other fibrous joint for similar purposes; excision of diseased tissue; and haemostasis.
The instruments of the invention are also useful for dissection, resection, vaporisation, desiccation and coagulation of tissue and combinations of these functions with particular application in urological endoscopic (urethroscopy, cystoscopy, ureteroscopy and nephroscopy) and percutaneous surgery. Urological procedures may include: electro-vaporisation of the prostate gland (EVAP) and other variants of the procedure commonly referred to as transurethral resection of the prostate (TURP) including, but not limited to, interstitial ablation of the prostate gland by a percutaneous or perurethral route whether performed for benign or malignant disease; transurethral or percutaneous resection of urinary tract tumours as they may arise as primary or secondary neoplasms and further as they may arise anywhere in the urological tract from the calyces of the kidney to the external urethral meatus; division of strictures as they may arise at the pelviureteric junction (PUJ), ureter, ureteral orifice, bladder neck or urethra; correction of ureterocoele; shrinkage of bladder diverticular; cystoplasty procedures as they pertain to corrections of voiding dysfunction; thermally induced shrinkage of pelvic floor as a corrective treatment for bladder neck descent excision of diseased tissue; and haemostasis.
Surgical procedures using the instrument of the invention include introducing the electrode assembly to the surgical site through an artificial conduit (a cannula), or through a natural conduit which may be in an anatomical body cavity or space or one created surgically. The cavity or space may be distended during the procedure using a fluid or may be naturally held open by anatomical structures. The surgical site may be bathed in a continuous flow of conductive fluid such as saline solution to fill and distend the cavity. The procedures may include simultaneous viewing of the site via an endoscope or using an indirect visualisation means.
Yet a further aspect of the invention provides an irrigated bipolar electrosurgical instrument that can be used in open air or gas-filled environments, in body fluids, or by insertion into tissue by the creation of a conductive fluid environment around the tip of the instrument.
Accordingly, the present invention provides an electrosurgical instrument for the treatment of tissue in the presence of an electrically-conductive fluid, the instrument comprising an instrument shaft and an electrode assembly at one end of the shaft, the electrode assembly comprising a tissue treatment electrode and a return electrode which is electrically insulated from the tissue treatment electrode by means of an insulation member, the tissue treatment electrode being exposed at the extreme distal end of the instrument, and the return electrode having a fluid contact surface spaced from the exposed end of the tissue treatment electrode by the insulation member, wherein the instrument further comprises feed means for feeding electrically-conductive fluid to the region of the exposed end of the tissue treatment electrode in such a manner as to define a conductive fluid path that completes, in use, an electrical circuit between the tissue treatment electrode and the return electrode.
In this way, it is possible to create a local conductive fluid environment around the tip of an electrosurgical instrument by delivering the fluid through the instrument in such a manner that the return electrode can be positioned remote from the tissue treatment electrode on or within the shaft of the instrument.
The electrode structure of this instrument thus simulates a monopolar configuration, with one active (tissue treatment) electrode and a remote return electrode, the return electrode being positioned on the instrument shaft to provide all the safety advantages of bipolar electrosurgery without the drawbacks. The separation of the two electrodes is supported by the delivery of the conductive medium, and allows higher powers to be delivered compared to conventional bipolar electrosurgery, but yet at power levels lower than conventional monopolar electrosurgery. The arrangement can also produce a contact vaporisation of tissue comparable to that of laser surgery.
The return electrode is spaced from the tissue treatment electrode so that, in use, it does not contact the tissue to be treated, and so that the electrical circuit is always completed by the conductive fluid, and not simply by arcing between the electrodes. Indeed, the arrangement is such that arcing between adjacent parts of the electrode assembly is avoided, thereby ensuring that the tissue treatment electrode can become enveloped in a vapour pocket so that tissue entering the vapour pocket becomes the preferred path for current to flow back to the return electrode via the conductive fluid.
In a preferred embodiment, the instrument further comprises removal means for removing electrically conductive fluid from the region of the exposed end of the tissue treatment electrode. The removal means is particularly important when the conductive fluid is a liquid such as saline, as saline heated up by the electrosurgical output needs to be removed to prevent the risk of collateral tissue damage.
By continually feeding electrically-conductive fluid such as saline to the region of the tissue treatment (active) electrode, and continually removing the fluid from this region, it is possible to create a local fluid field at the active electrode. Moreover, as fluid is constantly replenished in this region, the temperature of the active electrode can be maintained at a desired level.
In a preferred embodiment, the return electrode is a tubular member which is coated with an insulating sheath, the coated return electrode constituting the instrument shaft. Advantageously, the inner surface of the tubular member constitutes the return electrode. Preferably, the tubular member is made of stainless steel. In this case, the tissue treatment electrode may be supported centrally within the tubular member by an insulating spacer. Conveniently, the insulating spacer is made of a ceramic material, silicone rubber or glass.
The instrument may further comprise a tube extending proximally of the spacer. Preferably, the feed channel is constituted by the annular space between the return electrode and the tube, and the return channel is constituted by the interior of the tube and aperture means extending through the spacer. Alternatively, the instrument may further comprise a second return electrode constituted by a second tubular stainless steel member positioned concentrically within the first-mentioned tubular stainless steel member. In this case, the feed channel may be constituted by the annular space between the two return electrodes, and the return channel is constituted by the annular space between the second return electrode and the tube.
The invention also provides electrosurgical apparatus comprising a radio frequency generator and an electrosurgical instrument for treatment of tissue in the presence of an electrically-conductive fluid medium, wherein the electrosurgical instrument is as defined above.
The electrosurgical instrument of this aspect of the invention is useful for dissection, resection, vaporisation, dessication and coagulation of tissue and combinations of these functions with particular application in laparascopic, colposcopic (including vaginal speculum) and open surgical procedures on the female genital tract and adnexal related diseases. Laparascopic operative procedures may include: removal of subserosal and pedunculated fibroids, ablation of ectopic endometrium, ovarian cystectomy and ovarian drilling procedures; oophorectomy, salpingo-oophorectomy, subtotal hysterectomy and laparaoscopically assisted vaginal hysterectomy (LAVH) as may be performed for benign or malignant diseases; laparoscopic uterosacral nerve ablation (LUNA); fallopian tube surgery as correction of ectopic pregnancy or complications arising from acquired obstructions; division of abdominal adhesions; and haemostasis.
The electrosurgical instrument of the invention is also useful in the lower female genital tract, including treatment of cervix, vagina and external genitalia whether accessed directly or using instrumentation comprising generally speculae and colposcopes. Such applications include: vaginal hysterectomy and other pelvic procedures utilising vaginal access; LLETZ/LEEP procedure (large loop excision of the transformation zone) or excision of the transformation zone of the endocervix; removal of cystic or septic lesions; ablation of genital or venereal warts; excision of benign and malignant lesions; cosmetic and surgical repairs including vaginal prolapse; excision of diseased tissue; and haemostasis.
The electrosurgical instrument of this aspect of the invention is also useful for dissection, resection, vaporisation, desiccation and coagulation of tissue and combinations of these functions with particular application in surgery on the ear nose and throat (ENT) and more particularly procedures performed on the oropharynx, nasopharynx and sinuses. These procedures may be performed through the mouth or nose using speculae or gags or using endoscopic techniques such as functional endoscopic sinus surgery (FESS). Functional endoscopic sinus procedures may include: removal of chronically-diseased, inflamed and hypertrophic mucus linings, polyps and neoplasms from the various anatomical sinuses of the skull; excision of diseased tissue; and haemostasis. Procedures on the nasopharynx may include: removal of chronically-diseased, inflamed and hypertrophic mucus linings, polyps and neoplasms from the turbinates and nasal passages; submucus resection of the nasal septum; excision of diseased tissue; and haemostasis. Procedures on the oropharynx may include: removal of chronically-diseased, inflamed and hypertrophic tissue, polyps and neoplasms particularly as they occur related to the tonsil, adenoid, epigloific and supra-glottic regions, and salivary glands; as an alternative method to perform the procedure commonly known as laser assisted uvulopalatoplasty (LAUP); excision of diseased tissue; and haemostasis.
It is evident from the scope of applications of the invention that it has further additional applications for dissection, resection, vaporisation, desiccation and coagulation of tissue and combinations of these functions in general lapaaroscopic, thoracoscopic and neurosurgical procedures, being particularly useful in the removal of diseased tissue and neoplastic disease whether benign or malignant.
Surgical procedures using the electrosurgical instrument of the invention include introducing the electrode assembly to the surgical site whether through an artificial (cannula) or natural conduit which may be in an anatomical body cavity or space or one created surgically either using the instrument itself or by another technique. The cavity or space may be distended during the procedure using a fluid, or may be naturally held open by anatomical structures. The surgical site may be bathed in a continuous flow of conductive fluid, such as saline solution, to create a locally-irrigated environment around the tip of the electrode assembly in a gas-filled cavity or on an external body surface or other such tissue surfaces exposed during part of a surgical procedure. The irrigating fluid may be aspirated from the surgical site to remove products created by application of the RF energy, tissue debris or blood. The procedures may include simultaneous viewing of the site via an endoscope or using an indirect visualisation means.
The invention further provides a method of operating an electrosurgical apparatus having at least at tissue desiccation mode and a tissue vaporisation mode, the apparatus having a radio frequency generator coupled to an electrode assembly for the treatment of tissue in the presence of an electrically-conductive fluid medium, the electrode assembly comprising a tissue treatment electrode and a return electrode which is electrically insulated from the tissue treatment electrode by means of an insulation member, the tissue treatment electrode being exposed at the extreme distal end of the assembly, the return electrode having a fluid contact surface spaced from the exposed end of the tissue treatment electrode by the insulation member, the method comprising the steps of:
feeding electrically-conductive fluid to the region of the exposed end of the tissue treatment electrode; and
controlling the output power of the radio frequency generator to lie within a first output range for the tissue desiccation mode and to lie within a second range for the tissue vaporisation mode, the first output range being such that the power supplied to the electrode assembly maintains the conductive fluid adjacent to the tissue treatment electrode substantially at boiling point for tissue desiccation without creating a vapour pocket surrounding the tissue treatment electrode, and the second output range is such that the output power supplied to the electrode assembly for vaporisation of tissue is such as to maintain a vapour pocket surrounding the tissue treatment electrode.
Advantageously, the method further comprises the step of removing electrically-conductive fluid from the region of the exposed end of the tissue treatment electrode.
The invention still further provides an electrosurgical tissue desiccation method comprising the steps of:
providing an electrosurgical apparatus comprising a radio frequency generator coupled to an electrode assembly comprising a tissue treatment electrode and a return electrode, the tissue treatment electrode having an exposed distal end;
introducing the electrode assembly into a selected operation site with the tissue treatment electrode adjacent to the tissue to be treated;
feeding electrically-conductive fluid to the region of the exposed end of the tissue treatment electrode;
actuating the generator; and
controlling the radio frequency power supplied to the electrode assembly by the generator to maintain the conductive fluid adjacent to the tissue treatment electrode substantially at its boiling point without creating a vapour pocket surrounding the tissue treatment electrode.
In this case, the return electrode may be spaced proximally with respect to the tissue treatment electrode, and the electrode assembly may be introduced into the selected operation site such that the tissue treatment electrode is in contact with the tissue to be treated, and the return electrode is immersed in the electrically-conductive fluid, the electrode assembly being manipulated to cause heating and desiccation of the tissue in a required region adjacent to the tissue treatment electrode. Preferably, the electrode assembly is manipulated by moving the tissue treatment electrode across the surface of the tissue to be treated in a side-to-side xe2x80x9cpaintingxe2x80x9d technique.
The invention also provides an electrosurgical method comprising the steps of:
providing an electrosurgical apparatus comprising a radio frequency generator coupled to an electrode assembly comprising a tissue treatment electrode and a return electrode, the tissue treatment electrode having an exposed distal end;
introducing the electrode assembly into a selected operation site with the tissue contact electrode adjacent to the tissue to be treated;
feeding electrically-conductive fluid to the region of the exposed end of the tissue treatment electrode;
actuating the generator; and
applying sufficient radio frequency power to the electrode assembly to vaporise the electrically-conductive fluid surrounding the tissue treatment electrode to maintain a vapour pocket surrounding the tissue treatment electrode. Advantageously, the return electrode is spaced proximally with respect to the tissue treatment electrode, and the electrode assembly is introduced into the selected operation site""such that the tissue treatment electrode is positioned at least adjacent to the tissue to be treated, with the vapour pocket in contact with the tissue, and with the return electrode in contact with the electrically conductive fluid, the electrode structure being manipulated to achieve at least vaporisation of the tissue.